1. Field of the Invention
The present invention relates to control strategies for engines, and more particularly, to control strategies for rapidly heating an emission control device.
2. Background of the Invention
One method that has been used to heat an emission control device of an engine has been to operate some of the engine cylinders lean, and other cylinders rich. Then, when the exhaust gasses of these lean and rich cylinders mix, they can react over an activated catalyst. This catalytic reaction generates heat, thereby raising the temperature of the emission control device. Such an approach is described in U.S. Pat. No. 6,189,316.
However, the inventors herein have recognized a disadvantage with such an approach when the engine has first been started. In particular, just after an engine start, the catalyst is typically below a temperature that can support such an exothermic catalytic reaction. Further, the exhaust gasses from such lean and rich cylinders may not be high enough to support an exothermic reaction without a catalyst.